Gas compressor

Gas compressor

Overview
A gas compressor is a mechanical device that increases the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 of a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

 by reducing its volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....

.

Compressors are similar to pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

s: both increase the pressure on a fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

 and both can transport the fluid through a pipe
Pipe (material)
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases , slurries, powders, masses of small solids...

. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible; while some can be compressed, the main action of a pump is to pressurize and transport liquids.

The main types of gas compressors are illustrated and discussed below:



Compressors are often described as being either open, hermetic, or semi-hermetic, to describe how the compressor and motor
Motor
Motor is a device that creates motion. It usually refers to an engine of some kind. It may also specifically refer to:*Electric motor, a machine that converts electricity into a mechanical motion...

 drive is situated in relation to the gas or vapour being compressed.
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Encyclopedia
A gas compressor is a mechanical device that increases the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 of a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

 by reducing its volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....

.

Compressors are similar to pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

s: both increase the pressure on a fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

 and both can transport the fluid through a pipe
Pipe (material)
A pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases , slurries, powders, masses of small solids...

. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible; while some can be compressed, the main action of a pump is to pressurize and transport liquids.

Types of compressors


The main types of gas compressors are illustrated and discussed below:


Hermetically sealed, open, or semi-hermetic


Compressors are often described as being either open, hermetic, or semi-hermetic, to describe how the compressor and motor
Motor
Motor is a device that creates motion. It usually refers to an engine of some kind. It may also specifically refer to:*Electric motor, a machine that converts electricity into a mechanical motion...

 drive is situated in relation to the gas or vapour being compressed. The industry name for a hermetic is hermetically sealed compressor, while a semi- is commonly called a semi-hermetic compressor.

In hermetic and most semi-hermetic compressors, the compressor and motor driving the compressor are integrated, and operate within the pressurized gas envelope of the system. The motor is designed to operate and be cooled by the gas or vapour being compressed.

The difference between the hermetic and semi-hermetic, is that the hermetic uses a one-piece welded steel casing that cannot be opened for repair; if the hermetic fails it is simply replaced with an entire new unit. A semi-hermetic uses a large cast metal shell with gasketed covers that can be opened to replace motor and pump components.

The primary advantage of a hermetic and semi-hermetic is that there is no route for the gas to leak out of the system. Open compressors rely on either natural leather or synthetic rubber seals to retain the internal pressure, and these seals require a lubricant such as oil to retain their sealing properties.

An open pressurized system such as an automobile air conditioner can leak its operating gases, if it is not operated frequently enough. Open systems rely on lubricant in the system to splash on pump components and seals. If it is not operated frequently enough, the lubricant on the seals slowly evaporates, and then the seals begin to leak until the system is no longer functional and must be recharged. By comparison, a hermetic system can sit unused for years, and can usually be started up again at any time without requiring maintenance or experiencing any loss of system pressure.

The disadvantage of hermetic compressors is that the motor drive cannot be repaired or maintained, and the entire compressor must be removed if a motor fails. A further disadvantage is that burnt out windings can contaminate whole systems requiring the system to be entirely pumped down and the gas replaced. Typically hermetic compressors are used in low-cost factory-assembled consumer goods where the cost of repair is high compared to the value of the device, and it would be more economical to just purchase a new device.

An advantage of open compressors is that they can be driven by non-electric power sources, such as an internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

 or turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

. However, open compressors that drive refrigeration systems are generally not totally maintenance free throughout the life of the system, since some gas leakage will occur over time.

Centrifugal compressors



Centrifugal compressors use a rotating disk or impeller
Impeller
An impeller is a rotor inside a tube or conduit used to increase the pressure and flow of a fluid.- Impellers in pumps :...

 in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser
Diffuser
Diffuser can refer to any device that diffuses in some manner such as:* In aerodynamics** Diffuser , a shaped section of a car's underbody which improves the car's aerodynamic properties** divergent part of the flute...

 (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries
Oil refinery
An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...

, chemical
Chemical plant
A chemical plant is an industrial process plant that manufactures chemicals, usually on a large scale. The general objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials. Chemical plants use special equipment,...

 and petrochemical
Petrochemical
Petrochemicals are chemical products derived from petroleum. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as corn or sugar cane....

 plants and natural gas processing
Natural gas processing
Natural-gas processing is a complex industrial process designed to clean raw natural gas by separating impurities and various non-methane hydrocarbons and fluids to produce what is known as pipeline quality dry natural gas.-Background:...

 plants. Their application can be from 100 hp to thousands of horsepower. With multiple staging, they can achieve extremely high output pressures greater than 10000 psi (68.9 MPa).

Many large snowmaking
Snowmaking
Snowmaking is the production of snow by forcing water and pressurized air through a "snow gun" or "snow cannon", on ski slopes. Snowmaking is mainly used at ski resorts to supplement natural snow. This allows ski resorts to improve the reliability of their snow cover and to extend their ski...

 operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as supercharger
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...

s and turbocharger
Turbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...

s. Centrifugal compressors are used in small gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

 engine
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

s or as the final compression stage of medium sized gas turbines. Sometimes the capacity of the compressors is written in NM3/hr. Here 'N' stands for normal temperature pressure (20°C and 1 atm ) for example 5500 NM3/hr.

Diagonal or mixed-flow compressors


Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to an axial rather than radial direction.

Axial-flow compressors



Axial-flow compressors are dynamic rotating compressors that use arrays of fan-like airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....

s to progressively compress the working fluid. They are used where there is a requirement for a high flow rate or a compact design.

The arrays of airfoils are set in rows, usually as pairs: one rotating and one stationary. The rotating airfoils, also known as blades or rotors, accelerate the fluid. The stationary airfoils, also known as stators or vanes, decelerate and redirect the flow direction of the fluid, preparing it for the rotor blades of the next stage. Axial compressors are almost always multi-staged, with the cross-sectional area of the gas passage diminishing along the compressor to maintain an optimum axial Mach number
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

. Beyond about 5 stages or a 4:1 design pressure ratio, variable geometry
Variable geometry
Variable geometry may refer to:* Variable-geometry ways to alter the shape of an aircraft's wings in flight in order to alter their aerodynamic properties* Multi-speed Europe, a proposed strategy for European integration...

 is normally used to improve operation.

Axial compressors can have high efficiencies; around 90% polytropic at their design conditions. However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials. Axial-flow compressors can be found in medium to large gas turbine
Gas turbine
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

 engines, in natural gas pumping stations, and within certain chemical plants.

Reciprocating compressors



Reciprocating compressors use piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...

s driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...

 (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors well over 1000 hp are commonly found in large industrial and petroleum applications. Discharge pressures can range from low pressure to very high pressure (>18000 psi or 180 MPa). In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, and are typically larger, and more costly than comparable rotary units.
Another type of reciprocating compressor is the swash plate compressor, which uses pistons which are moved by a swash plate mounted on a shaft - see Axial Piston Pump
Axial piston pump
An axial piston pump is a positive displacement pump that has a number of pistons in a circular array within a cylinder block. It can be used as a stand-alone pump, a hydraulic motor or an automotive air conditioning compressor.-Description:...

.

Household, home workshop, and smaller job site compressors are typically reciprocating compressors 1½ hp or less with an attached receiver tank.

Rotary screw compressors



Rotary screw compressors use two meshed rotating positive-displacement helical screws
Helix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...

 to force the gas into a smaller space. These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 hp to over 1200 hp and from low pressure to moderately high pressure (>1200 psi or 8.3 MPa).

Rotary screw compressors are commercially produced in Oil Flooded, Water Flooded and Dry type.

Rotary vane compressors


Rotary vane compressors consist of a rotor with a number of blades inserted in radial slots in the rotor. The rotor is mounted offset in a larger housing which can be circular or a more complex shape. As the rotor turns, blades slide in and out of the slots keeping contact with the outer wall of the housing. Thus, a series of decreasing volumes is created by the rotating blades. Rotary Vane compressors are, with piston compressors one of the oldest of compressor technologies.

With suitable port connections, the devices may be either a compressor or a vacuum pump. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Dry vane machines are used at relatively low pressures (e.g., 2 bar or 200 kPa; 29 psi) for bulk material movement while oil-injected machines have the necessary volumetric efficiency to achieve pressures up to about 13 bar (1,300 kPa; 188.5 psi) in a single stage. A rotary vane compressor is well suited to electric motor drive and is significantly quieter in operation than the equivalent piston compressor.

Rotary vane compressors can have mechanical efficiencies of about 90%.

Scroll compressors



A scroll compressor, also known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

 or compress fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....

s such as liquids and gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

es. The vane geometry may be involute
Involute
In the differential geometry of curves, an involute is a curve obtained from another given curve by attaching an imaginary taut string to the given curve and tracing its free end as it is wound onto that given curve; or in reverse, unwound. It is a roulette wherein the rolling curve is a straight...

, archimedean spiral
Archimedean spiral
The Archimedean spiral is a spiral named after the 3rd century BC Greek mathematician Archimedes. It is the locus of points corresponding to the locations over time of a point moving away from a fixed point with a constant speed along a line which rotates with constant angular velocity...

, or hybrid curves. They operate more smoothly, quietly, and reliably than other types of compressors in the lower volume range.

Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid or gas between the scrolls.

This type of compressor was used as the supercharger
G-Lader
The G-Lader is a scroll-type supercharger used in various Volkswagen Passenger Cars models. Its purpose is to increase the motive power output from the internal combustion engine attainable with a given engine displacement. Since it is not enough to simply inject more fuel, as this produces too...

 on Volkswagen G60 and G40 engines in the early 1990s.

Diaphragm compressors


A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in contact with the gas being compressed.

The degree of flexing and the material constituting the diaphragm affects the maintenance life of the equipment. Generally stiff metal diaphragms may only displace a few cubic centimeters of volume because the metal can not endure large degrees of flexing without cracking, but the stiffness of a metal diaphragm allows it to pump at high pressures. Rubber or silicone diaphragms are capable of enduring deep pumping strokes of very high flexion, but their low strength limits their use to low-pressure applications, and they need to be replaced as plastic embrittlement occurs.

Diaphragm compressors are used for hydrogen and compressed natural gas (CNG
Compressed natural gas
Compressed natural gas is a fossil fuel substitute for gasoline , diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill...

) as well as in a number of other applications.

The photograph included in this section depicts a three-stage diaphragm compressor used to compress hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gas to 6000 psi (41.4 MPa) for use in a prototype compressed hydrogen
Compressed hydrogen
Compressed hydrogen is the gaseous state of the element hydrogen kept under pressure. Compressed hydrogen in hydrogen tanks at 350 bar and 700 bar is used for mobile hydrogen storage in hydrogen vehicles...

 and compressed natural gas
Compressed natural gas
Compressed natural gas is a fossil fuel substitute for gasoline , diesel, or propane/LPG. Although its combustion does produce greenhouse gases, it is a more environmentally clean alternative to those fuels, and it is much safer than other fuels in the event of a spill...

 (CNG) fueling station built in downtown Phoenix, Arizona
Phoenix, Arizona
Phoenix is the capital, and largest city, of the U.S. state of Arizona, as well as the sixth most populated city in the United States. Phoenix is home to 1,445,632 people according to the official 2010 U.S. Census Bureau data...

 by the Arizona Public Service
Arizona Public Service
Arizona Public Service Company is the largest electric utility in Arizona and the principal subsidiary of publicly-traded S&P 500 member Pinnacle West Capital Corporation , which in turn had been formerly named AZP Group, when Arizona Public Service reorganized as that holding company in 1985.With...

 company (an electric utilities company). Reciprocating compressor
Reciprocating compressor
A reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases at high pressure....

s were used to compress the natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...

.

The prototype alternative fuel
Alternative fuel
Alternative fuels, known as non-conventional or advanced fuels, are any materials or substances that can be used as fuels, other than conventional fuels...

ing station was built in compliance with all of the prevailing safety, environmental and building codes in Phoenix to demonstrate that such fueling stations could be built in urban areas.

Air bubble compressor


Also known as a trompe
Trompe
A trompe is a water-powered gas compressor, commonly used before the advent of the electric-powered compressor. A trompe is somewhat like an airlift pump working in reverse....

. A mixture of air and water generated through turbulence is allowed to fall into a subterranean chamber where the air separates from the water. The weight of falling water compresses the air in the top of the chamber. A submerged outlet from the chamber allows water to flow to the surface at a lower height than the intake. An outlet in the roof of the chamber supplies the compressed air to the surface. A facility on this principal was built on the Montreal River
Montreal River (Timiskaming District, Ontario)
The Montreal River is a river in Timiskaming District, Ontario, Canada. It travels from its source at Smoothwater Lake to its mouth at Lake Timiskaming on the Ottawa River. The river is a significant source of hydroelectricity.-Course:...

 at Ragged Shutes near Cobalt, Ontario
Cobalt, Ontario
Cobalt is a town in the district of Timiskaming, province of Ontario, Canada, with a population of 1,223 In 2001 Cobalt was named "Ontario's Most Historic Town" by a panel of judges on the TV Ontario program Studio 2, and in 2002 the area was designated a National Historic Site.-History:Silver was...

 in 1910 and supplied 5,000 horsepower to nearby mines.

Temperature


Compression of a gas naturally increases its temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

, often referred to as the heat of compression.

where



so



with n taking different values for different compression processes (see below).
  • Adiabatic
    Adiabatic process
    In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which the net heat transfer to or from the working fluid is zero. Such a process can occur if the container of the system has thermally-insulated walls or the process happens in an extremely short time,...

     - This model assumes that no energy (heat) is transferred to or from the gas during the compression, and all supplied work is added to the internal energy of the gas, resulting in increases of temperature and pressure. Theoretical temperature rise is:


with T1 and T2 in degrees Rankine or kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...

s, and k = ratio of specific heat
Heat capacity ratio
The heat capacity ratio or adiabatic index or ratio of specific heats, is the ratio of the heat capacity at constant pressure to heat capacity at constant volume . It is sometimes also known as the isentropic expansion factor and is denoted by \gamma or \kappa . The latter symbol kappa is...

s (approximately 1.4 for air). Rc is the compression ratio; being the absolute outlet pressure divided by the absolute inlet pressure. The rise in air and temperature ratio means compression does not follow a simple pressure to volume ratio. This is less efficient, but quick. Adiabatic compression or expansion more closely model real life when a compressor has good insulation, a large gas volume, or a short time scale (i.e., a high power level). In practice there will always be a certain amount of heat flow out of the compressed gas. Thus, making a perfect adiabatic compressor would require perfect heat insulation of all parts of the machine. For example, even a bicycle tire pump's metal tube becomes hot as you compress the air to fill a tire.
The relation between temperature and compression ratio described above means that the value of n for an adiabatic process is k (the ratio of specific heats).
  • Isothermal
    Isothermal process
    An isothermal process is a change of a system, in which the temperature remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir , and the change occurs slowly enough to allow the system to continually adjust to the temperature of the reservoir...

     - This model assumes that the compressed gas remains at a constant temperature throughout the compression or expansion process. In this cycle, internal energy is removed from the system as heat at the same rate that it is added by the mechanical work of compression. Isothermal compression or expansion more closely models real life when the compressor has a large heat exchanging surface, a small gas volume, or a long time scale (i.e., a small power level). Compressors that utilize inter-stage cooling between compression stages come closest to achieving perfect isothermal compression. However, with practical devices perfect isothermal compression is not attainable. For example, unless you have an infinite number of compression stages with corresponding intercoolers, you will never achieve perfect isothermal compression.


For an isothermal process, n is 1, so the value of the work integral for an isothermal process is:



When evaluated, the isothermal work is found to be lower than the adiabatic work.
  • Polytropic - This model takes into account both a rise in temperature in the gas as well as some loss of energy (heat) to the compressor's components. This assumes that heat may enter or leave the system, and that input shaft work can appear as both increased pressure (usually useful work) and increased temperature above adiabatic (usually losses due to cycle efficiency). Compression efficiency is then the ratio of temperature rise at theoretical 100 percent (adiabatic) vs. actual (polytropic). Polytropic compression will use a value of n between 0 (a constant-pressure process) and infinity (a constant volume process). For the typical case where an effort is made to cool the gas compressed by an approximately adiabatic process, the value of n will be between 1 and k.

Staged compression


In the case of centrifugal compressors, commercial designs currently do not exceed a compression ratio of more than a 3.5 to 1 in any one stage (for a typical gas). Since compression generates heat, the compressed gas is to be cooled between stages making the compression less adiabatic and more isothermal. The inter-stage coolers typically result in some partial condensation that is removed in vapor-liquid separator
Vapor-liquid separator
A vapor–liquid separator is a device used in several industrial applications to separate a vapor–liquid mixture.For the common variety, gravity is utilized in a vertical vessel to cause the liquid to settle to the bottom of the vessel, where it is withdrawn....

s.

In the case of small reciprocating compressors, the compressor flywheel may drive a cooling fan that directs ambient air across the intercooler of a two or more stage compressor.

Because rotary screw compressors can make use of cooling lubricant to remove the heat of compression, they very often exceed a 9 to 1 compression ratio. For instance, in a typical diving compressor the air is compressed in three stages. If each stage has a compression ratio of 7 to 1, the compressor can output 343 times atmospheric pressure (7 × 7 × 7 = 343 atmosphere
Atmosphere (unit)
The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...

s). (343 standard atmosphere)

Prime movers


There are many options for the "prime mover" or motor which powers the compressor:
  • gas turbine
    Turbine
    A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

    s power the axial and centrifugal flow compressors that are part of jet engine
    Jet engine
    A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

    s
  • steam turbine
    Steam turbine
    A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....

    s or water turbine
    Water turbine
    A water turbine is a rotary engine that takes energy from moving water.Water turbines were developed in the 19th century and were widely used for industrial power prior to electrical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy...

    s are possible for large compressors
  • electric motor
    Electric motor
    An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

    s are cheap and quiet for static compressors. Small motors suitable for domestic electrical supplies use single phase alternating current
    Alternating current
    In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....

    . Larger motors can only be used where an industrial electrical three phase
    Three-phase electric power
    Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by grids worldwide to transfer power. It is also used to power large motors and other heavy loads...

     alternating current supply is available.
  • diesel engine
    Diesel engine
    A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber...

    s or petrol engine
    Petrol engine
    A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol and similar volatile fuels....

    s are suitable for portable compressors and support compressors. Common in automobiles and other types of vehicles (including piston-powered airplanes, boats, trucks, etc.), diesel or gasoline engines can power compressors using their own crankshaft power (this setup known as a supercharger
    Supercharger
    A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...

    ), or, using their waste exhaust gas to spin a turbine connected to the compressor (this setup known as a turbocharger
    Turbocharger
    A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...

    ).

Applications


Gas compressors are used in various applications where either higher pressures or lower volumes of gas are needed:
  • in pipeline transport
    Pipeline transport
    Pipeline transport is the transportation of goods through a pipe. Most commonly, liquids and gases are sent, but pneumatic tubes that transport solid capsules using compressed air are also used....

     of purified natural gas to move the gas from the production site to the consumer. Often, the compressor in this application is driven by a gas turbine which is fueled by gas bled from the pipeline. Thus, no external power source is necessary.
  • in petroleum refineries, natural gas processing plants, petrochemical and chemical plants, and similar large industrial plants for compressing intermediate and end product gases.
  • in refrigeration
    Refrigeration
    Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...

     and air conditioner equipment to move heat
    Heat
    In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

     from one place to another in refrigerant
    Refrigerant
    A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...

     cycles: see Vapor-compression refrigeration
    Vapor-compression refrigeration
    Vapor-compression refrigeration is one of the many refrigeration cycles available for use. It has been and is the most widely used method for air-conditioning of large public buildings, offices, private residences, hotels, hospitals, theaters, restaurants and automobiles...

    .
  • in gas turbine systems to compress the intake combustion
    Combustion
    Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

     air
  • in storing purified or manufactured gases in a small volume, high pressure cylinders for medical, welding
    Welding
    Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

     and other uses.
  • in many various industrial, manufacturing and building processes to power all types of pneumatic tools.
  • as a medium for transferring energy
    Energy
    In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

    , such as to power pneumatic equipment.
  • in pressurised
    Cabin pressurization
    Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...

     aircraft to provide a breathable atmosphere of higher than ambient pressure.
  • in some types of jet engine
    Jet engine
    A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

    s (such as turbojets and turbofan
    Turbofan
    The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan...

    s) to provide the air required for combustion of the engine fuel. The power to drive the combustion air compressor comes from the jet's own turbine
    Turbine
    A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

    s.
  • in SCUBA diving
    Scuba diving
    Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....

    , hyperbaric oxygen therapy
    Hyperbaric oxygen therapy
    Hyperbaric medicine, also known as hyperbaric oxygen therapy , is the medical use of oxygen at a level higher than atmospheric pressure. The equipment required consists of a pressure chamber, which may be of rigid or flexible construction, and a means of delivering 100% oxygen...

     and other life support devices to store breathing gas
    Breathing gas
    Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...

     in a small volume such as in diving cylinder
    Diving cylinder
    A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....

    s.
  • in surface supplied diving
    Surface supplied diving
    Surface supplied diving refers to divers using equipment supplied with breathing gas using a diver's umbilical from the surface, either from the shore or from a diving support vessel sometimes indirectly via a diving bell...

     an air compressor is frequently used to supply low pressure air (10 to 20 bar) to the diver for breathing
  • in submarine
    Submarine
    A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

    s, to store air for later use in displacing water from buoyancy chambers, for adjustment of depth.
  • in turbocharger
    Turbocharger
    A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...

    s and supercharger
    Supercharger
    A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...

    s to increase the performance of internal combustion engine
    Internal combustion engine
    The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...

    s by increasing mass flow.
  • in rail
    Rail transport
    Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...

     and heavy road transport
    Road transport
    Road transport or road transportation is transport on roads of passengers or goods. A hybrid of road transport and ship transport is the historic horse-drawn boat.-History:...

     to provide compressed air
    Compressed air
    Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....

     for operation of rail vehicle brakes
    Air brake (rail)
    An air brake is a conveyance braking system actuated by compressed air. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on March 5, 1872. The Westinghouse Air Brake Company was subsequently organized to manufacture and sell...

     or road vehicle brakes
    Air brake (road vehicle)
    Air brakes are used in trucks, buses, trailers, and semi-trailers. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Originally designed and built for use on railroad train application, air brakes remain the exclusive systems...

     and various other systems (door
    Door
    A door is a movable structure used to open and close off an entrance, typically consisting of a panel that swings on hinges or that slides or rotates inside of a space....

    s, windscreen wiper
    Windscreen wiper
    A windscreen wiper or windshield wiper is a device used to remove rain and debris from a windscreen or windshield. Almost all motor vehicles, including trains, aircraft and watercraft, are equipped with such wipers, which are usually a legal requirement.A wiper generally consists of an arm,...

    s, engine
    Engine
    An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

    /gearbox control, etc.).
  • in miscellaneous uses such as providing compressed air for filling pneumatic tire
    Tire
    A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...

    s.
  • in the case of the fire piston
    Fire piston
    A fire piston, sometimes called a fire syringe, is a device of ancient origin which is used to kindle fire. It uses the principle of the heating of a gas by its rapid compression to ignite a piece of tinder, which is then used to set light to kindling.-Description and use:A fire piston consists...

     and the heat pump
    Heat pump
    A heat pump is a machine or device that effectively "moves" thermal energy from one location called the "source," which is at a lower temperature, to another location called the "sink" or "heat sink", which is at a higher temperature. An air conditioner is a particular type of heat pump, but the...

    , the desired outcome is the temperature rise of the gas, and compressing the gas is only a means to that end.

See also


  • Cabin pressurization
    Cabin pressurization
    Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude.-Need for cabin pressurization:...

  • Centrifugal fan
    Centrifugal fan
    A centrifugal fan is a mechanical device for moving air or other gases. It has a fan wheel composed of a number of fan blades, or ribs, mounted around a hub. As shown in Figure 1, the hub turns on a driveshaft that passes through the fan housing...

  • Compressed air
    Compressed air
    Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....

  • Electrochemical hydrogen compressor
    Electrochemical hydrogen compressor
    An electrochemical hydrogen compressor is a hydrogen compressor where hydrogen is supplied to the anode, and compressed hydrogen is collected at the cathode with an exergy efficiency of 70 to 80% for pressures up to 10,000 psi or 700 bars.-Principle:...

  • Fire piston
    Fire piston
    A fire piston, sometimes called a fire syringe, is a device of ancient origin which is used to kindle fire. It uses the principle of the heating of a gas by its rapid compression to ignite a piece of tinder, which is then used to set light to kindling.-Description and use:A fire piston consists...

  • Foil bearing
    Foil bearing
    Foil bearings, also known as foil-air bearings, are a type of air bearing. A shaft is supported by a compliant, spring-loaded foil journal lining. Once the shaft is spinning quickly enough, the working fluid pushes the foil away from the shaft so that there is no more contact...

  • Gas compression heat pump
  • Guided rotor compressor
    Guided rotor compressor
    The guided rotor compressor is a positive displacement rotary gas compressor. The compression volume is defined by the trochoidally rotating rotor mounted on an eccentric drive shaft with a typical 80 to 85% adiabatic efficiency.-History:...

  • Hydrogen compressor
    Hydrogen compressor
    A hydrogen compressor is a device that increases the pressure of hydrogen by reducing its volume. Compression of hydrogen gas naturally increases its temperature, due to Charles' Law....

  • Ionic liquid piston compressor
    Ionic liquid piston compressor
    An ionic liquid piston compressor, ionic compressor or ionic liquid piston pump is a hydrogen compressor based on an ionic liquid piston instead of a metal piston as in a piston-metal diaphragm compressor.-Principle:...


  • Linear compressor
    Linear compressor
    A linear compressor is a gas compressor where the piston moves along a linear track to compress to minimize energy loss during conversion.-History:...

  • Liquid ring compressor
    Liquid ring
    A liquid ring pump is a rotating positive displacement pump. They are typically used as a vacuum pump but can also be used as a gas compressor....

  • Hydride compressor
    Hydride compressor
    A hydride compressor is a hydrogen compressor based on metal hydrides with absorption of hydrogen at low pressure and desorption of hydrogen at high pressure by raising the temperature with an external heat source like a heated waterbed or electric coil....

  • Natterer compressor
    Natterer compressor
    A Natterer compressor was a type of air compression machine which was used in early experiments in making liquid oxygen in the 1870s. A manually operated screw jack was utilized to compress air or other gases up to ~200 atm ....

  • Pneumatic cylinder
    Pneumatic cylinder
    Pneumatic cylinders are mechanical devices which utilize the power of compressed gas to produce a force in a reciprocating linear motion....

  • Pneumatic tube
    Pneumatic tube
    Pneumatic tubes are systems in which cylindrical containers are propelled through a network of tubes by compressed air or by partial vacuum...

  • Roots blower (a lobe-type compressor)
  • Tuyau
    Tuyau
    A tuyau is an ancient invention for producing cool, dry compressed air from a flow of water. It is a remarkable device because it can produce almost any degree of compression, given deep enough water, and has no moving parts or seals to wear.A pipe is constructed. One end of the pipe points...

    -Trompe
    Trompe
    A trompe is a water-powered gas compressor, commonly used before the advent of the electric-powered compressor. A trompe is somewhat like an airlift pump working in reverse....

  • Vapor-compression refrigeration
    Vapor-compression refrigeration
    Vapor-compression refrigeration is one of the many refrigeration cycles available for use. It has been and is the most widely used method for air-conditioning of large public buildings, offices, private residences, hotels, hospitals, theaters, restaurants and automobiles...

  • Variable speed air compressor
    Variable speed air compressor
    A variable-speed drive air compressor is an air compressor that takes advantage of variable-speed drive technology. This type of compressor uses a special drive to control the speed of the unit, which in turn saves energy compared to a fixed speed equivalent.The most common form of VSD...